PM / OPP Introduce APIs to remove OPPs

OPPs are created statically (from DT) or dynamically. Currently we don't free
OPPs that are created statically, when the module unloads. And so if the module
is inserted back again, we get warning for duplicate OPPs as the same were
already present.

Also, there might be a need to remove dynamic OPPs in future and so API for that
is also added.

This patch adds helper APIs to remove/free existing static and dynamic OPPs.

Because the OPPs are used both under RCU and SRCU, we have to wait for grace
period of both. And so are using kfree_rcu() from within call_srcu().
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/opp.c

@@ -79,6 +79,7 @@ struct dev_pm_opp {
  *		however addition is possible and is secured by dev_opp_list_lock
  * @dev:	device pointer
  * @srcu_head:	notifier head to notify the OPP availability changes.
+ * @rcu_head:	RCU callback head used for deferred freeing
  * @opp_list:	list of opps
  *
  * This is an internal data structure maintaining the link to opps attached to
@@ -90,6 +91,7 @@ struct device_opp {
 
 	struct device *dev;
 	struct srcu_notifier_head srcu_head;
+	struct rcu_head rcu_head;
 	struct list_head opp_list;
 };
 
@@ -498,6 +500,76 @@ int dev_pm_opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
 }
 EXPORT_SYMBOL_GPL(dev_pm_opp_add);
 
+static void kfree_opp_rcu(struct rcu_head *head)
+{
+	struct dev_pm_opp *opp = container_of(head, struct dev_pm_opp, rcu_head);
+
+	kfree_rcu(opp, rcu_head);
+}
+
+static void kfree_device_rcu(struct rcu_head *head)
+{
+	struct device_opp *device_opp = container_of(head, struct device_opp, rcu_head);
+
+	kfree(device_opp);
+}
+
+void __dev_pm_opp_remove(struct device_opp *dev_opp, struct dev_pm_opp *opp)
+{
+	/*
+	 * Notify the changes in the availability of the operable
+	 * frequency/voltage list.
+	 */
+	srcu_notifier_call_chain(&dev_opp->srcu_head, OPP_EVENT_REMOVE, opp);
+	list_del_rcu(&opp->node);
+	call_srcu(&dev_opp->srcu_head.srcu, &opp->rcu_head, kfree_opp_rcu);
+
+	if (list_empty(&dev_opp->opp_list)) {
+		list_del_rcu(&dev_opp->node);
+		call_srcu(&dev_opp->srcu_head.srcu, &dev_opp->rcu_head,
+			  kfree_device_rcu);
+	}
+}
+
+/**
+ * dev_pm_opp_remove()  - Remove an OPP from OPP list
+ * @dev:	device for which we do this operation
+ * @freq:	OPP to remove with matching 'freq'
+ *
+ * This function removes an opp from the opp list.
+ */
+void dev_pm_opp_remove(struct device *dev, unsigned long freq)
+{
+	struct dev_pm_opp *opp;
+	struct device_opp *dev_opp;
+	bool found = false;
+
+	/* Hold our list modification lock here */
+	mutex_lock(&dev_opp_list_lock);
+
+	dev_opp = find_device_opp(dev);
+	if (IS_ERR(dev_opp))
+		goto unlock;
+
+	list_for_each_entry(opp, &dev_opp->opp_list, node) {
+		if (opp->rate == freq) {
+			found = true;
+			break;
+		}
+	}
+
+	if (!found) {
+		dev_warn(dev, "%s: Couldn't find OPP with freq: %lu\n",
+			 __func__, freq);
+		goto unlock;
+	}
+
+	__dev_pm_opp_remove(dev_opp, opp);
+unlock:
+	mutex_unlock(&dev_opp_list_lock);
+}
+EXPORT_SYMBOL_GPL(dev_pm_opp_remove);
+
 /**
  * opp_set_availability() - helper to set the availability of an opp
  * @dev:		device for which we do this operation
@@ -687,4 +759,34 @@ int of_init_opp_table(struct device *dev)
 	return 0;
 }
 EXPORT_SYMBOL_GPL(of_init_opp_table);
+
+/**
+ * of_free_opp_table() - Free OPP table entries created from static DT entries
+ * @dev:	device pointer used to lookup device OPPs.
+ *
+ * Free OPPs created using static entries present in DT.
+ */
+void of_free_opp_table(struct device *dev)
+{
+	struct device_opp *dev_opp = find_device_opp(dev);
+	struct dev_pm_opp *opp, *tmp;
+
+	/* Check for existing list for 'dev' */
+	dev_opp = find_device_opp(dev);
+	if (WARN(IS_ERR(dev_opp), "%s: dev_opp: %ld\n", dev_name(dev),
+		 PTR_ERR(dev_opp)))
+		return;
+
+	/* Hold our list modification lock here */
+	mutex_lock(&dev_opp_list_lock);
+
+	/* Free static OPPs */
+	list_for_each_entry_safe(opp, tmp, &dev_opp->opp_list, node) {
+		if (!opp->dynamic)
+			__dev_pm_opp_remove(dev_opp, opp);
+	}
+
+	mutex_unlock(&dev_opp_list_lock);
+}
+EXPORT_SYMBOL_GPL(of_free_opp_table);
 #endif

include/linux/pm_opp.h

@@ -21,7 +21,7 @@ struct dev_pm_opp;
 struct device;
 
 enum dev_pm_opp_event {
-	OPP_EVENT_ADD, OPP_EVENT_ENABLE, OPP_EVENT_DISABLE,
+	OPP_EVENT_ADD, OPP_EVENT_REMOVE, OPP_EVENT_ENABLE, OPP_EVENT_DISABLE,
 };
 
 #if defined(CONFIG_PM_OPP)
@@ -44,6 +44,7 @@ struct dev_pm_opp *dev_pm_opp_find_freq_ceil(struct device *dev,
 
 int dev_pm_opp_add(struct device *dev, unsigned long freq,
 		   unsigned long u_volt);
+void dev_pm_opp_remove(struct device *dev, unsigned long freq);
 
 int dev_pm_opp_enable(struct device *dev, unsigned long freq);
 
@@ -90,6 +91,10 @@ static inline int dev_pm_opp_add(struct device *dev, unsigned long freq,
 	return -EINVAL;
 }
 
+static inline void dev_pm_opp_remove(struct device *dev, unsigned long freq)
+{
+}
+
 static inline int dev_pm_opp_enable(struct device *dev, unsigned long freq)
 {
 	return 0;
@@ -109,11 +114,16 @@ static inline struct srcu_notifier_head *dev_pm_opp_get_notifier(
 
 #if defined(CONFIG_PM_OPP) && defined(CONFIG_OF)
 int of_init_opp_table(struct device *dev);
+void of_free_opp_table(struct device *dev);
 #else
 static inline int of_init_opp_table(struct device *dev)
 {
 	return -EINVAL;
 }
+
+static inline void of_free_opp_table(struct device *dev)
+{
+}
 #endif
 
 #endif		/* __LINUX_OPP_H__ */